Dehydration of castor oil



United States p O of castor oil.

This invention relates to aprocess for the dehydration Castor oil, the triglyceride of ahydroxylated iafatty acid, is a non-drying oil and has limited use in coating compositions. Its non-drying property is due to the fact that the fatty acid contains only one double .bondper molecule whereas the fatty acids of drying oils contain two or three double bonds per molecule. By'heating castor oil or its fatty acids to high temperatures thehyg droxyl group is split oif in the form of water and .a;-sec

ond double bond is introduced into the fatty .acid rnolecule. As a result, dehydrated castor oil is a drying oil and is of considerable value in coatingscompositions;v Many processes of dehydrating Castor oil either directly or indirectly through the separated fatty: acid have I been suggested and the simplest of these is merely toheat a batch of the oil in a kettle, to between 260 d goo'g t: t at which temperature dehydration will take place, the batch at that temperature until the req i d1d V of dehydration is obtained, and'then'allow thebat h 56 cool down. Although the process may beaccelerated by means of catalysts it still takesseveral hours 'andis notj wholly satisfactory since prolonged heating of the oil atthe high temperatures. involved results in decomposition and polymerisation of the dehydrated oil. 1 Decomposition reduces the yield, and polymerisation beyond a certain degree results in anoil unsuitableffor the manufacture of monoglycerides to be used in alkyd resins.

If, in an attempt to increase production, the size-of batch is increased then the elfect of these secondary and undesirable reactions becomes more pronounced: heat transfer requirements make-itgdifiicult rapidly to heat and cool large batches: and the result'isthatthe oil is maintained at high periods. t -1 According to the present inventioncaster; oil is dehytemperatures for; undesirably long drated by a process comprising continuously-massing 've'ssel tin castor oil and a dehydration catalyst into;. which the mixture is vigorouslygagitated and"maintained at a temperature of 260 375?, C., the treated-oil being withdrawn at such a rate as 'to'maintain asubstantially constant volume of liquid in the vessel,gthe ratio of 'said volume to the volume of castor being from 0.521 to 10.021.

The oil and catalyst maybe passedfinto'thetdehydration vessel either separately or as amixture.

In order to obtain a goodtdegree of dehydration in oil added per: minute the short reaction times of the present inventionfit is desirable that the water produced inthe course of the reaction should be removed from the reaction mixture as rapidly as possible. To facilitate evolution oftthe water, vapour the pressure at which the reaction is carried out should be not substantially greater than atmospheric and,

where a particularlyhigh degree of dehydration is re-, quired, may advantageously be less than atmospheric. It: is also preferred that the reaction be carried outtin a vessel in which the reaction mixture has a free exposed surface through which the water vapour maybe con-I t ;I ,Patented June 21, t 1955 tinuously 'evolved during the reaction rather than in :a confined space'as in, say,atubular type of reactor. The ratio oil volume: oil input ,jrna be termed; the average reaction time: and; since in our invention this tim'e referred to. above are reduced to minimum; In particut a el min ed t nib iq rp o es 7 slpossible to de hydrate castor oiljto aj degree an viscosity of the dehydrated {oil being not 7 u -ppise' ;at,;2s,,c;, Suchadehydratedgjcastor oil has not before been producedion a commercial scale. "An, advantage'offour process is thatlthecastor oil on v'enterin'gitlre vessel is substantially instantaneously heated to reaction I temperature and since itcan berapidly cooled on leaving;

the-vessel it is maintained atan elevated T temperature only with dehydration of large bat'ches'of voil are avoided and yet high rat'e's of output maybe achievedf t V Fania 'I t w r flApot-like ve'ssellofe /s gallon working :capae y with .tainin'g'them at128 5l C; was usedtodehydratetcastor'oil containing asi catalyst 0.8% by weight of concentrated sulphuric acid. :The oil and catalystf were; premixed fiat I V roomattemperaturegand thetmixture wasirun int'o'uthe drawn on into a condenseribymeans 'of an astor "oil having the following constants Li li-ma KOH/ "1,37 poises at 25 0;

Refractive index; T, I. V.- (Woburn) Colour The rate offoutput compares of fknown batch proce cyclef'fo r p V I equivalent to' a rate 1of productionjoflll 'galloniper' hour {per gallon capacity of theWesselij 'ln' gthe continuous process 'described above {the rate of; productionf '56 vesseljf gallons hour 1 per gallon capa "ity fot v V Ex qi'mpletjI t v t The process describedgin Example II. was usedftoQdehy-J dratet castor'oillicontaining as catalyst l.6%;,by-weight of' concentrated fllsulphuric' acid. With a reacto'r tem perature of 310 .C. the output obtained .was 6 gals/hour 1 of dehydr ated castor oil having the following. constants: Acid value- Viscosity r. I. v. wanna -1'.26,poises at 25 C a t su pi r by increasl gf'the workingTcapacityof the dehydration vessel.i;I-Iowev er, larr important feature of the" process is that -hig h rates er input of cold oil demand It thefvesselis lrettle shaped then'as its size'is increased itsfworking capacity increases, at; ajmuch' greater rate than the heat-transfer area -The rate-:of oil inputibeing dependant upon "the heat-,transfrfarea a,pointtissoon t) is .so very. short the efiects of the secondaryt reactions 1 q ym i i n1' i s shydrt m ybe sub ne 1 t an 8 he V.

rno re than ,1.5

i for a minimum period duringwhich tdehydrationris ef- ,fected; it The disadvantages of long heating up and cooling 1 V down periods andjthe lack of precise control associated means-for vigorously agitating the contentsaand for main-"- reaction vessel at a constant rate; The :efiluent was if t m m t' of e 'iflla 0 C- g I which theErate-pf; olymerisation Of thedehydratedoil .fijThe jvapours'jevolved from the "reaction The output obtained ,wa-1' a1's./ hour of I 34.4 mgms. Kori/ i A being I a correspondingly highrate of heat input into the vessel; a

reached at which the low oil volume: oil input ratio characteristic of thisinventionis diffieult to maintain. For very high rates of output then it is preferable to operate a series of small vessels connected in parallel. Alternatively, a trough-shaped vessel may be used, the oil flow being across and not along the axis of the trough.

The heat input demands in the dehydration vessel may be reduced by preheating the castor oil feed but where this is added in admixture with the catalyst, the mixture should not be maintained at a preheat temperature of more than 100 C. for long periods, otherwise the efiects of the reactions which occur at these temperatures will become considerable, and the character of the process, namely, the relatively short period of heat-treatment, will tend to be lost. The maximum length of time permissible will depend on the actual temperatures and on the nature and proportion of the catalyst;

Example III Cold castor oil mixed with 0.4% by weight of concentrated sulphuric acid was continuously passed through a heat exchanger in which its temperature was raised to 180 C. and then into a pot-like reaction vessel of 6 gallons working capacity. In the reaction vessel the mixture was vigorously stirred and maintained at a temperature of 275 C. The dehydrated oil overflowed through an outlet in the side of the vessel and passed back into the heat exchanger wherein heating up the incoming castor oil, it was cooled to below 200* C. Water vapour and other volatile matter produced in the reaction vessel was led ofi through a wide fume duct into a condenser. The output obtained was 40 gals/hour of dehydrated castor oil having the following constants:

Acid value l 13.7 mgms. KOH/gm. OH value, 49 mgrns. 'KOH/gm. Viscosity 1.90 poisesat 25 C. Colour n 2.5 P. R. S. units.

The .diflicuities of premature reaction which may occur in preheating catalysed oil may be avoided by preheating uncatalysed oil and adding the catalyst, preferably diluted with a further quantity of cold or moderately Warm oil, to the mixture in the reaction vessel.

', i Example IV To a pot-like vessel of /45 gallon working capacity were continuously added raw castor oil at a temperature of 285 C. and a .cold mixture of raw castor oil with 2% by weight of concentrated sulphuric acid, the proportion of hot :oil to cold oil being .411. The reaction mixture was vigorously agitated and maintained at a temperature of 350 C.,, the evolved vapour-s being drawn ofi through a condenser. The overflow of oil irom the vessel was rapidly cooled o below 200 C. and he ou pu was 0 gallons/hour of dehydrated castor oil having the following constants:

Acid value; 1-0.2 .mgms. KOH/gm. OH value 43.0 mgms. K'OH/gm. Viscosity 1.38 poise at 25 C. Colour 3.5 P. R. S. units.

tation in the vessel prevents build-up of the catalyst but in general, liquids, for example sulphuric, phosphoric and phosphorous acids are preferred. Sulphonic acid catalysts such as benzene sulphonic acid and chlorsulphonic acid may be used though their efficiency is rather less than that of sulphuric acid. .Chlorsnlphonic acid in particular is notable since like phosphorous acid it gives a paler dehydrated oil than does sulphuric acid. Due to the oil/catalyst mixture being maintained at an elevated te perature for only a short time, it is possible to use oncentrations o catal s h her than tho us d in at h processes. This in turn results in shorter reaction times being made p s th gh the h con en a of some catalysts may considerably darken the dehydrated oil. However, in the temperature'range above 300 C. a good degree of dehydration :may beobtained in a short reaction time without having to use the higher catalyst concentrations and under these conditions, as is shown in Example IV, it is possible to produce a very low vis cosity dehydrated oil of good colour.

What we claim is: i

l. A process of dehydrating castor oil comprising continuously passing castor oil and a dehydration catalyst into a vessel in which the mixture is vigorously agitated and maintained at a temperature of 260375 C., the treated oil being withdrawn from the vessel at such a rate as to maintain a substantially constant volume of liquid in the vessel, the ratio of the said volume to the volume of castor oil added per minute being from 0.5:1 to 10.021,

and the castor oil withdrawn from the vessel being at least about 85% dehydrated.

2. A process as claimed in claim 1 in which the dehydration reaction is carried out at a pressure not substantially greater than atmospheric.

3, A process as claimed in .claim 1 in which the reaction mixture has a free exposed surface through which the water vapour produced may be continuously evolved during the reaction.

4. A process as claimed in vclaim l in which the dehydration reaction is carried out at a temperature above 300 ,5, A process as claimed in claim 1 in which the dehydrated oil withdrawn from the vessel is rapidly cooled to a temperature below 200' C. i I

6. A process as claimed in claim '1 in which at leas part of the oil is preheated before entering the reaction vessel.

7. A processas claimed in claim 6 in which the oil is preheated in the absence of catalyst.

8. A process as claimed in claim '1 in which the catalyst isconcentrated sulphuric acid.

9. A process as claimed in claim 1 in which increased output is obtained by employing a plurality of vessels in parallel.

10. A process of dehydrating castor oil comprising continuously passing castor oil and a dehydration catalyst into a vessel in which the mixture is vigorously agitated and maintained at a temperature of 260 to 375 C., the treatedoil being withdrawn from the vessel at such a rate as to maintain a substantially constant volume of liquid in-the vessel, the ratio of the said volume to the volume of castor oil added per minute being from 0.5 :1 to 10.0:1. References Cited in the file of this :patent UNITED STATES PATENTS Miller Oct. 7, 19.47 Colbeth Sept. .8, 1-951 

10. A PROCESS OF DEHYDRATING CASTOR OIL COMPRISING CONTINUOUSLY PASSING CASTOR OIL AND A DEHYDRATION CATALYST INTO A VESSEL IN WHICH THE MIXTURE IS VIGOIOUSLY AGITATED AND MAINTAINED AT A TEMPERATURE OF 26* TO 375* C., THE TREATED OIL BEING WITHDRAWN FROM THE VESSEL AT SUCH A RATE AS TO MAINTAIN A SUBSTANTIALLY CONSTANT VOLUME OF LIQUID IN THE VESSEL, THE RATIO OF THE SAID VOLUME TO THE VOLUME OF CASTOR OIL ADDED PER MINUTE BEING FROM 0.5:1 TO 10.0:1. 